The difference between hot rolled galvanized sheet and cold rolled galvanized sheet
In the regular trading of galvanized sheets, cold-rolled basic galvanization is the main one, and hot-rolled substrates are relatively rare. Then, what is the difference between hot-rolled substrates and cold-rolled substrates galvanized products? Let's make a simple interpretation from the following aspects
Because there is one less process than the cold-rolled substrate, the production cost of galvanizing the hot-rolled substrate is lower than that of the cold rolling, mainly due to the annealing cost and the cold rolling cost, and the other processes are similar.
Quality & Performance
Because the hot-rolled substrate is only pickled and annealed to remove surface impurities, its surface is relatively rough, the adhesion of the zinc layer is better, and the thickness of the coating is biased toward 140/140g/m2. However, the thickness dimension is not as high as that of cold rolling. Since most of them are thick zinc layers, the thickness of the zinc layer is not uniformly controlled. There is little difference in mechanical properties, and some properties are even better than cold rolling.
Hot-rolled base plate galvanized sheet is not as good as cold-rolled base plate because of its dimensional accuracy and surface quality, and the thickness is thicker than cold-rolled galvanized sheet, so it is often used for structural members with low surface requirements but high strength and thickness requirements.
For example, the structural parts of washing machines, refrigerators and other household appliances, automobile internal structural parts, automobile chassis structural parts, passenger car body, roof, highway guardrail, cold-formed steel, etc.
Because the cost of hot-rolled galvanized sheet is low, and as the technology progresses, the thickness of the specifications is getting larger and larger, and the amount of use is gradually increasing.
Common grades of hot-rolled galvanized sheet are DD51D+Z, HD340LAD+Z, HR340LA, HR420LA, HR550LA, etc.;
The cold-rolled galvanized sheet corresponds to DC51D+Z, HC340LAD+Z, HC340LA, HC420LA, HC550LA, etc.;
There is also a grade that does not specify whether it is cold-rolled or hot-rolled substrate, such as DX51D+Z. Generally, this grade can be considered as hot-rolled galvanized sheet.
Hot Rolled vs Cold Rolled Steel
Steel comes in many grades, specifications, shapes, and finishes—the World Steel Association lists over 3,500 different grades of steel, each with unique properties. The various types mean that steel can by widely used in infrastructure, appliances, vehicles, wind turbines, and many more applications.
Optimizing steel’s properties for each application goes beyond changing the chemical composition, however. The manufacturing processing of steel can also have a significant impact on steel products—even when the grades and specifications are the same. One key distinction among pre-fabricated steel products is the difference between hot rolled and cold rolled steel.
It’s important to note that the main difference between hot rolled and cold rolled steel is one of process. “Hot rolling” refers to processing done with heat. “Cold rolling” refers to processes done at or near room temperature. Although these techniques affect overall performance and application, they should not be confused with formal specifications and grades of steel, which relate to metallurgical composition and performance ratings. Steels of different grades and specifications can be either hot rolled or cold rolled—including both basic carbon steels and other alloy steels. Knowing which to use can help avoid over-spending on raw materials. It can also save time and money on additional processing. Understanding the differences between hot and cold steel is integral to choosing one over the other.
热轧钢Hot rolled steel
Hot rolled steel is steel that has been roll-pressed at very high temperatures—over 1,700˚F, which is above the re-crystallization temperature for most steels. This makes the steel easier to form, and resulting in products that are easier to work with.
To process hot rolled steel, manufacturers first start with a large, rectangular length of metal, called a billet. The billet is heated and then sent for pre-processing, where it is flattened into a large roll. From there, it is kept at a high temperature and run through a series of rollers to achieve its finished dimensions. The white-hot strands of steel are pushed through the rollers at high speeds. For sheet metal, rolled steel is spun into coils and left to cool. For other forms, such as bars or plates, materials are sectioned and packaged.
Steel shrinks slightly as it cools. Since hot rolled steel is cooled after processing, there is less control over its final shape, making it less suitable for precision applications. Hot rolled steel is often used in applications where minutely specific dimensions aren’t crucial. Railroad tracks and construction projects often use hot rolled steel.
Hot rolled steel can often be identified by the following characteristics:
A scaled surface—a remnant of cooling from extreme temperatures
Slightly rounded edges and corners for bar and plate products (due to shrinkage and less precise finishing)
Slight distortions, where cooling may result in slightly trapezoidal forms, as opposed to perfectly squared angles
Hot rolled steel typically requires much less processing than cold rolled steel, which makes it a lot cheaper. Because hot rolled steel is allowed to cool at room temperature, it’s essentially normalized—meaning it’s free from internal stresses that can arise from quenching or work-hardening processes.
Hot rolled steel is ideal where dimensional tolerances aren’t as important as overall material strength, and where surface finish isn’t a key concern. Where surface finish is a concern, scaling can be removed by grinding, sand blasting, or acid-bath pickling.
冷轧钢Cold rolled steel
Cold rolled steel is essentially hot rolled steel that has been through further processing. Once hot rolled steel has cooled, it is then re-rolled at room temperature to achieve more exact dimensions and better surface qualities.
Cold rolled steel can often be identified by the following characteristics:
Better, more finished surfaces with closer tolerances
Smooth surfaces that are often oily to the touch
Bars are true and square, and often have well-defined edges and corners
Tubes have better concentric uniformity and straightness
With better surface characteristics than hot rolled steel, it’s no surprise that cold rolled steel is often used for more technically precise applications, or where aesthetics are important. But due to the additional processing for cold finished products, they come at a higher price.
In terms of physical characteristics, cold rolled steels are typically harder and stronger than standard hot rolled steels. As the metal is shaped at the lower temperatures, the steel’s hardness, resistance against tension breaking, and resistance against deformation are all increased due to work hardening.
These additional treatments, however, can also create internal stress within the material. This can cause unpredictable warping if the steel is not stress relieved prior to cutting, grinding, or welding.
For more information on steel, or to request a quote for a custom project, please contact us.
Hot-dip galvanizing process characteristics
There are many processes that use zinc to prevent corrosion of steel, such as: electro-galvanizing process, the thickness of the zinc layer is generally controlled at 5 ~ 15μm; the blown hot-dip galvanizing process (this book refers to "blow plating", the same below), the galvanized layer is more Thickness, generally less than 35μm; the thickness of the galvanized layer of the hanging plating process is more than 65μm, and some products require the thickness of the galvanized layer to be as high as 100μm or more. For large steel structures and box sections (this book is unified as "cavity workpieces" ", the same below) For steel structures, the thickness of the galvanized layer is larger.
The hot-dip galvanizing process has good coverage, the galvanized layer is dense, without organic inclusions, and its corrosion protection or corrosion resistance is much higher than that of electro-galvanized; however, for the hanging plating process, the thickness of the galvanized layer has a higher value. The lower limit of thickness, that is to say, the galvanized layer is too thin, but it is not easy to achieve; for the blow plating process, according to the technical index requirements of profiles, pipes, etc., the control of the thickness of the galvanized layer is relatively more flexible .
The protective effect of the galvanized layer on steel is twofold. First, the galvanized layer with good penetration resistance completely isolates the protected steel from the corrosive environment, thereby completely eliminating one of the main conditions for steel corrosion, that is, "electrolyte" . Secondly, because zinc is more chemically active than steel, it is more likely to be corroded and dissolved (the principle of sacrificial anode). Once the galvanized layer is locally damaged and the surface of the steel is exposed, zinc becomes an anode, which corrodes before steel, so as to achieve In order to protect the steel.
In the electrochemical protection, compactness, durability, maintenance-free of the galvanized layer, the bonding force of the galvanized layer and the steel matrix, the economics of the galvanized layer, and the adaptability of the hot-dip galvanizing process to the shape and size of the workpiece, the production Compared with all aspects such as high efficiency, the hot-dip galvanizing process has the unparalleled and unique advantages of other metal corrosion protection processes.
Introduction to the classification and use of galvanized sheet.
Galvanized steel sheet according to the production process can be divided into the following categories:
1.Hot dip galvanized steel sheet. The steel sheet is immersed in a molten zinc bath to adhere a zinc-plated steel sheet to the surface. At present, it is mainly produced by a continuous galvanizing process, that is, a coiled steel plate is continuously immersed in a plating tank in which zinc is melted to form a galvanized steel sheet.
2.Alloyed galvanized steel sheet. This steel sheet is also produced by hot dip, but immediately after it is taken out, it is heated to about 500 ° C to form an alloy coating of zinc and iron. This galvanized sheet has good adhesion and weldability of the coating.
3.Electro-galvanized steel plate. The production of such a galvanized steel sheet by electroplating has good workability. However, the coating is thinner and the corrosion resistance is not as good as that of hot dip galvanized sheet.
4.Single-sided plating and double-sided differential galvanized steel. Single-sided galvanized steel, that is, a product that is only galvanized on one side. It has better adaptability than double-sided galvanized sheet in welding, painting, anti-rust treatment and processing. In order to overcome the shortcomings of uncoated zinc on one side, there is a galvanized sheet coated with a thin layer of zinc on the other side, that is, a double-sided differential galvanized sheet.
5.Alloy, composite galvanized steel sheet. It is made of zinc and other metals such as lead, zinc alloy or even composite plated steel. This steel plate has excellent rust resistance and good coating properties.
In addition to the above five types, there are also colored galvanized steel sheets, printed galvanized steel sheets, and polyvinyl chloride laminated galvanized steel sheets. However, the most commonly used ones are still hot dip galvanized sheets.
Galvanized steel sheets can be further divided into galvanized steel sheets for general use, roofing, exterior panels for buildings, structural, tiled slabs, tensile and deep drawing.
Galvanized sheet is widely used in automobile industry, construction industry, furniture manufacturing, transportation and other industries.
Galvanized sheet is used in the construction industry: roof, roof prefabricated components, living balcony control panel, balcony, book kiosk, warehouse, electric rolling shutter door, electric heater, precipitation pipeline, etc.
Galvanized sheet is used in electrical products: refrigerator, automatic washing machine, high voltage switch cabinet, air conditioner, microwave oven heating, bread maker, printer, vending machine, electric fan, vacuum cleaner, etc.
Galvanized sheet is used in home decoration industry: lamp cover, wardrobe, dining table, bookcase，etc.
Galvanized sheet is used in transportation and manufacturing industry: Car ceiling, car shell, truck board, tractor, electric vehicle, shipping container, cargo ship compartment board, etc.
Galvanized sheet is used in other aspects: traditional musical instrument case, trash can, billboard, bank counter, clock, medical equipment, photographic equipment, meter, etc.
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What is Success?
In our societies, we use the word success a lot.
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People who are tying fear are also big success stories.
No one can be successful at everything.
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There are always sacrifices.
It's great to be successful.
It is even better to make sure you followed your own distinctive and not necessarily always obvious path to the success that can truly fulfill you
Middle East client visit
On the end of November, 2018, one Middle East clients come to visit our company office----Rogosteel. He have visit China for many times, and a “China Expert”. Before this visit, we have been discuss about order for a long time.
At about 13:00pm, He arrived our office by taxi, and we spend one hour to do further discussion, and show the sample. He is satisfied with our products, and give us the order details to quote. We talked a lot dyring our meeting, make us know better for each other. After this, he bring one piece of our sample to his factory to do some test.
We will do more better during communicate with your customers, and grow together.